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    <title>Document</title>
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<body>
   <!-- 20.编写一个函数 ，要求传入一个字符串参数 ，首字母改大写 --> 
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<script>
 function fun(str){
    document.write(str[0].toUpperCase("h")+str.slice(1))
  }
  var str=fun("hi")
</script>
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